Furnace for the combustion of lignite and semibituminous coal



Feb. 20, 1940. 0, s. BOWMAN 2,190,973 FURNACE FOR THE COMBUSTION 0F LIGNITE AND sEMIBITUMINoUs COAL Filed Aug. 29, 1938 /n ver? for O//ver -3 50h/mah Patented Feb. 20, 1940` FURNACE FOR THE COMBUSTIOjN OF LIG- NITE AND SEMIBITUMINOUS COAL OliverSBowman, Colorado Springs, Colo.

` Application `August 29,

4 claims.

This invention relates to improvements iri furnaces and has reference more particularly to furnaces for the combustion of lignite and semibituminous coal. It has been estimated that over fty percent of the coal inthe United States is comprised of two different gradesof lignite. This'type of coal diiers greatly from anthracite and bituminous coal and requires different types of furnaces for l0 their most eflicient combustion. Lignite coal slacks very easily and crumbles quite readily when subjected to heat and therefore offers great resistance to the passage ofl air,thereby making it difficult to procure eicient combustion. Ex l with the greatestelciency in layers from two to four inches thick and that if the coal is positioned between spaced `verticali grates so as to form a thin vertical wallthat is ignited at the zo. bottom and the air necessary for combustion is passed through this wall of coal, a highly efflcient combustion is obtained. Since the com` bustion takes place at the lower end of the wall the ashes will drop down `and will not clog the` employ a straight vertical` wall of coal, it is `madecylir'idrical by lernplcying spaced concentric cylindrical grates in the manner to be here- .indescribed 0 It is theobject of this invention to produce a furnace having concentric `cylindrical grates spaced apart so as to `provide an annular cylindrical space for the reception of the solid fuel and `to so arrange the air supply and the draft that the air `will flow transversely through the layer of coal. l

` Another object is to providea grate construction which will keep the openings in the grates o from clogging and which willpermit the ash to be readily removed vand the consumed fuel replaced.

A further object is toproduce a furnace in which heated air is mixed with the gaseous prod- `ucts of combustion so as to oxidize any carbonaceous material presentin the gases Aand thus preventsmoke, and in addition obtain the heat resulting from the oxidation.

The above and other objects that maybecome apparent as this description proceeds are obtained by means of a construction and an arrangement of parts that will nowbe described` in de-` tail and for this purpose reference will be had to the accompanying drawing in which the in 5gzvention has been illustrated and in which f perience hasshown that lignite coal can be burned i938, `serial No. 227,325

Figure l is a verticardiametricalcross section `through a" furnaceembodying the invention;

Figure 2 is a transverse section taken on 'line 2 2, Fig. 1; l

Figure 3 is a fragmentary view, similar to the Yone shown in Fig. l, and shows a differentffeed` device;

Figure 4 is a fragmentary view, similar to the f one shown in Fig-l,` and shows how a forced draft can be applied;

Figure 5 is an inside elevation of one section of the inner grate;

Figure 6` is a transverse section taken on line 6 6, Fig. 5;

i Figure 'l is a `vertical section taken on line 1'l, Fig. 5;

Figure 8 is an elevation showing the outside of a sectionof the outer` grate.

Fig. 8, and H Figure 10 is a section taken cn line lillit Fig. 8. l l

In the drawing the invention has been shown as embodied in a furnace having a circular com-` bustion chamber formedby a Awall* `l`l`I of fire brick. A grate support ring'IZ `is built into the inner surfaceof the Wall and has an inwardly projecting flange i3 on which an `annular grate `I4 is supported. The central opening in the grate is closedby a circular dump grate l5. A pinion I6, secured to the inner end lof shaft El engages with teeth on` the under surface of the grate and when shaft I 'i is oscillated the grate will also be` oscillated. The furnace wall has been shown as provided with an ash compartment door I8 and cleanout openings provided with suitable closures I9. In the embodiment shown in Fig. l the gaseous products of combustion have been shown as escaping through flue 20 but the drawing is illustrative only and the heated gases may pass through an opening 2l and thence through the flues of aboiler or other` heat interchange apparatus. i i

A cylindrical grate,1 constructed from a plu.- rality of sections 22 like those shown in Figs. 8, 9 and 10, is supported from ring l2, each grate section has two `outwardly projecting lugs 23 at its lower end, which extend over the. gratev ring in the manner shown in Fig. 1. The vertical "section engages the groove in the next section` Each grate` so as to form a cylindrical grate.` section` is also provided with` an.v outwardly cir-- tending flange 23a along each vertical edge which engages the inner surface of the brick wall and these flanges serve to space the outer surface of the grate a predetermined distance from the inner surface of the brick wall to form passages or channels 26 for the escape of the gases of combustion. YIt will be observed that each grate section is providedwith a row of elongated opencfs. burned in layers' of any thickness and` it is thereings 2l that are vertically spaced an-d extend transversely of the grate. From Fig.. 10 it will be seen that the slots 2l are upwardly and outwardly inclinedl and that there are downwardly inclined overhanging lips 28 above each slot.

The inner grate is formed from a plurality of` grate sections 29,-similar in lmany respects to sections 22 but having a greater curvature.

ception of stove bolts .whereby the several sections necessary to` form a complete cylinder can be held in assembled relation; four, six` or any other number of sections can be used. In the embodiment illustrated four sections have been shown. Sections 29 are also provided with transverse slots 2'I that are upwardly and inwardly inclined and have overhanginglips 23.` Each section 29 is provided at its upper end with two 'v upwardly and inwardly inclined. perforated lugs provided and this communicates with a pipe 35 o f refractory material whose lower end terminates directly above the vertex of the conical cover, a slide 36 serves to cut off the flow of coal when necessary. When the fire is started the kindling is placed at the bottom of the anular space between the two concentric grates and this space is then filled with coal. Since the nre begins to burn at the lower edge ofthe coal and progresses upwardly, the coal willmove downwardly by the actions of gravity so as to automatically replace the fuel as it is consumed, and final stagerof the combustion takes place on the grate and the ash and the clinkers, if any,` either rest on or pass downwardly through grate I4.

Since the air for combustion is supplied from -the inside of the inner grate it will pass transversely through the layer of coal and the gaseousl products of combustion will flow upwardly through channels 26. If any combustible gases are present among those owing upwardly through channel 26 they will be consumed when they come in contact with the air which as- .sures high efficiency and smokeless operation.

With this `combustion chamber the coal can be fore possible to burn lignite slack or other slack because air for, combustion cany always passV through the thin layer.

`The inner grate projects into such close proximity tothe upper surface of grate I4 that a throat is formed that prevents any great amount of coal from flowing downwardly along the upper surface of grate I4 when the latter is stationary. Some live coals do cover the upper surface of- EachI section is provided with inwardlyl extending" radial lugs 30, which are perforated for the re y grate I4 on which the nal stages of the combustion take place.

. s The dump grate is preferably provided with a tube 3l that provides a freer air passage even if the surrounding grate surfacebecomes clogged. If it is found desirable to employ forced draft, the lower lend of the inner grate is closed by means of a plate 33 and an air duct 39 provided which connects the interior ofthe .inner grate with afan which'hasbeen indicated by dotted lines at 40.

If a gravity feed like that shown in Fig.. l

`'is found to be undesirable, a mechanical trickle feed likev that shown in Fig. 3 can be used. In

this typeof feed the coal isconveyed from a suitable hopper by a `screw ill which is preferably operat'edby a thermostatically controlled motor which has not been" shown. The -coal flows downwardly in tubev 42 and is distributed by th cone cover 32.

It will be observed that ltheair slots 2l cannot choke and become ineffective because they in-I oline downwardly towards the coal and are. fur-` thermore protected 'by lthe overhangingv lipsy 28.,

The specific `construction of the grates is not material as the same results may be obtained polygonal one but it' is evident that the method here explained can be practised with specifically` different-shapes of combustionjspaces so long yas means is 'provided for holding thecoal in the..

shape of a thin wall sofpositioned that combustion takes place from the bottom and air isr forced transversely through ythe wall of coal.

The inclination of slots Wand thel overhanging lips 28, are structural features of importance as they assure that the air will have free passage at alltimes.

The grates are preferably made from cast iron but may bemadefrom llire clay ory any other suitablematerial.v f K It is, of course, to Abe understood. that the combustion mayv take place all along the layer of coal from the bottom to the top. Since the coal is ignited "at the bottom itisevidentthat the combustion is completed at the bottom first and progresses upwardly. The gases-are driven off near the top of the grates and passinto the channel or channels 26 where they come into contact with heated air supplied through vpipes 33 and are consumed.A y. v l s V Grate I4 can beoscillated by the means shown and described and clinkers can be dumped fby tilting grate I5. I

of channels it is possible to channel or space 26.

In the drawing an embodiment has been` shown in which the airis fed to the inside of the innergrate and passes outwardly through the fuel.4

A reversal of this can readily be made in which the air is admitted to channel 26 and the gaseous products of combustion are renewed` from the interior of the inner grate.

sliders thatthis is7 included in the scope of. -his invention. l

vHaving described the invention what isy claimed as new is:

Such reversal may! be desirable 1n some cases and applicant con' Although space 261s divided into a plurality;

have `one annular top of the inner grate, and tubular air ducts attached at their inner ends to the cover and having their outer ends resting on and extending across the outer grate for supporting the inner grate and into the space outside of the outer grate for the purpose of conveying heated air to the outside surface of the outer grate.

2. A combustion chamber for the burning of solid carbonaceous fuel, comprisingin combination, two concentric, vertically positioned cylindrical grates, spaced apart to forman annular cylindrical fuel space, a wall surrounding the outer grate and spaced therefrom to form a passage for the gaseous products of combustion, a

cover attached to the upper end of" the inner grate, the grates having slots extending circumferentially, means comprising tubes for supporting the inner grate from the outer grate and for conducting heated air from the top of the inner grate to the gas passages outside of the outer grateto complete the combustion of the gases.

3. A furnace for the combustion of carbona- Ceous fuel comprising, in combination, a cylindrical enclosing Wall of refractory material, a grate ring positioned in the inner surface of the wall, a

` cylindrical grate supported on the grate ring with its outer surface spaced from the inner surface of the wall toform a channel for the escape of gaseous products of combustion, an inner cylindrical grate positioned within the rst grate and spaced therefrom to provide an annular fuel space, a cover attached to the top of the inner i grate, and a plurality of tubular members radiating from the cover, said tubular members communicating with the interior of the inner grate at one end and with the channel surrounding the outer grate at the other end, thetubular mern- `wal1, a cylindrical grate supported `on the grate ring with its outer surface spaced from the inner surface of the wall to form a channel for the escape of gaseous products of combustion, an

inner cylindrical grate positioned within the first grate and spaced therefrom to provide an annular fuel space, a cover attached to the inner grate, means for feeding fuel to the fuel space,

` means for introducing air into the inner grate;

the air passing from the interior of the inner grate through the fuel, products ofv combustion .passing through the outer grate and into the `space between the outer surface of the outer grate and the inner surface of the wall, and conduits connecting the interior of the inner grate i with the top of the channel, whereby air is provided to complete thecombustion of any combustible material in the gaseous products of cornbustion, said conduits serving also to support the inner grate from the top of the outer grate.

OLIVER S. BOWMAN. 

